This invention relates, in generally, to an apparatus for selectively monitoring radar signals impinging on a moving vehicle and providing an alert responsive thereto and, in particular, to an apparatus for selectively monitoring radar signals only when the vehicle is traveling above a preselected speed.
Without limiting the scope of the present invention, its background will be described with reference to radar detectors used to alert drivers to the use of speed-determining radar devices as an example.
Law enforcement officials commonly use speed-determining radar devices to monitor the speed of motor vehicles traveling on roads and highways. The speed-determining radar devices emit electromagnetic radiation in specific bands of the radio-frequency spectrum. Specifically, speed-determining radar devices typically emit electromagnetic radiation in the X band (10.50 Ghz to 10.55 Ghz), the Ku band (13.40 Ghz to 13.50 Ghz), the K band (24.05 Ghz to 24.25 Ghz) and the Ka band (33.40 Ghz to 36.00 Ghz).
Accordingly, radar detectors used to alert drivers to the use of speed-determining radar devices must be able to sweep the entire radio-frequency spectrum of interest and issue an alert upon detection of a radar signal within one of the specific bands. Since the frequencies emitted by the speed-determining radar devices are high, typical radar detectors use a superheterodyne radio receiver that mixes the received radio-frequency signal with a local oscillator signal. The heterodyning of these signals produces two intermediate frequency signals whose frequencies are the sum and difference of the radio-frequency signal frequency and the local oscillator signal frequency. Since the difference intermediate frequency is typically desired, the difference frequency is separated from the sum frequency using a filter. Thereafter, the filtered intermediate frequency signal may be amplified and used to alert the driver, via audible signals, visual signals and the like to the use of a speed-determining radar device.
It has been found, however, that the use of such superheterodyne radio receivers to mix radio-frequency signals with a local oscillator signal may result in spurious emission of portions of the local oscillator signal from the radar detector. These spurious emissions have been linked to interference in the spectral proximity of the local oscillator signal. For example, it has been suggested that these spurious emissions interfere with communication between satellites and earth-based satellite transceivers. Interesting, this interference has been particularly noted near intersections when vehicles having radar detectors are traveling at low speeds or are at rest.
In some prior radar detectors used to alert drivers to the use of speed-determining radar devices, anti-false alarm systems have been implemented. Specifically, U.S. Pat. No. 5,977,884 issued Nov. 2, 1999 to Ross discloses a radar detecting circuit adapted to be on a vehicle to detect a radar signal and selectively provide a radar detect signal in response to detecting the radar signal. In the Ross system, the vehicle""s speed is determined by a tachometer signal or a global positioning system receiver adapted to be on the vehicle which provides a speed signal representative of the vehicle speed. An alarm responsive to both the radar detect signal and the speed signal provides an alarm indication when a radar signal is detected and the vehicle speed is above a preset maximum, such as the speed limit. The operator of the Ross detector may set the present maximum speed via an input device such as a keypad or via voice recognition software.
Similarly, U.S. Pat. No. 6,204,798 issued Mar. 20, 2001 to Fleming, III discloses a radar detector for alerting an operator of a motor vehicle to an incoming police radar signal. In the Fleming system, the radar detector includes a microprocessor, a circuit coupled to the microprocessor for detecting the incoming police radar signal and a global positioning system receiver coupled to the microprocessor. Upon detection of an incoming radar signal, the radar detector can utilize the position, velocity and/or heading data from the global positioning system receiver to determine whether to generate an alert.
While both of these designs minimize unnecessary alerts if the vehicle is traveling below a specified speed, neither of these systems addresses the problem of spurious emissions from radar detectors positioned in vehicles traveling at low speed or at rest. In both systems, the incoming radar signals are constantly monitored and processed regardless of the speed at which the vehicle is traveling. According, radar detectors made from these designs may contribute to interference in the spectral proximity of their local oscillator signals even when the vehicles are traveling at low speed or are at rest.
Therefore, a need has arisen for a radar detector that alerts drivers to the use of speed-determining radar devices and has a reduced likelihood of causing interference in the spectral proximity of the local oscillator signal. A need has also arisen for such a radar detector that selectively monitors radar signals such that spurious emissions of the local oscillator signal are selectively prevented when a vehicle having such a radar detector is traveling at a low speed or is at rest.
The present invention disclosed herein comprises an apparatus and method for alerting a driver to the use of speed-determining radar devices that reduces likelihood of interference in the spectral proximity of the local oscillator signal. The apparatus and method of the present invention achieve this result by selectively monitoring radar signals from speed-determining radar devices only when the vehicle is traveling above a preselected speed. Accordingly, spurious emissions of the local oscillator signal are selectively prevented when a vehicle having an apparatus of the present invention operating therein is traveling at a speed below the preselected speed.
The apparatus for selectively monitoring radar signals of the present invention comprises a speed determination circuit that determines the speed of the vehicle and provides a speed signal representative thereof to a comparator. The speed determination circuit may be, for example, a global positioning system receiver or a circuit processing a speed signal sent from the vehicle. In either case, the comparator compares the speed signal to a preselected speed and provides an on signal when the vehicle speed exceeds the preselected speed and an off signal when the vehicle is at or below the preselected speed. The preselected speed may be zero or may be a speed greater than zero.
The signal generated the comparator, either the on signal or the off signal, is then sent to a radar detecting circuit. When the radar detecting circuit received the on signal, the radar detecting circuit is powered such that it may detect radar signals originating from a radar source remote from the vehicle. When such radar signals are detected, the radar detecting circuit processes the radar signals by, among other things, mixing the radar signals with a local oscillator signal. After processing the radar signals, the radar detecting circuit generates a radar detected signal, which is provided to an alarm. The alarm, in response to the radar detected signal, provides an alert to the driver of the vehicle of the use of a speed-determining radar device. Alternatively, if the radar detecting circuit received the off signal from the comparator, the radar detecting circuit is not powered. Accordingly, no spurious emission from the radar detecting circuit occurs.
Broadly stated, the method of the present invention involves determining the vehicle speed, determining whether the vehicle speed exceeds a preselected speed and detecting the radar signals only if the vehicle speed exceeds the preselected speed. More specifically, the method of the present invention involves determining the vehicle speed and generating a speed signal representative thereof, comparing the speed signal with a preselected speed, generating an on signal if the vehicle speed exceeds the preselected speed and generating an off signal if the vehicle speed is at or below the preselected speed, receiving the radar signals with an antenna, generating a local oscillator signal that is mixed with the radar signals to generate a radar detected signal, if the on signal is generated and providing an alert if the radar detected signal is generated.